Electrolytic apparatus and surface treatment method using the same

ABSTRACT

An electrolytic apparatus that is used for a workpiece having an irregular cross-sectional shape, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof, the electrolytic apparatus includes a mounting section that closes a lower opening of the workpiece, a holding section that closes an upper opening of the workpiece, and an electrode that is placed inside the workpiece, the electrode having a hollow cross-sectional shape, and having a plurality of jet orifices for discharging an electrolyte solution respectively toward the plurality of recesses of the workpiece, and the mounting section and/or the holding section having a plurality of drain outlets that are provided respectively corresponding to the plurality of recesses of the workpiece.

BACKGROUND

The present invention relates to an electrolytic apparatus that maysuitably be used to treat the inner surface of a workpiece having anirregular hollow cross-sectional shape, and a surface treatment methodusing the same.

A number of pieces of surface treatment apparatus for treating only theinner surface of a workpiece having a hollow section have been proposed.

For example, Japanese Patent No. 4886555 discloses an inner surfacetreatment apparatus for a cylindrical member. According to the innersurface treatment apparatus, the upper opening and the lower opening ofthe cylindrical member are closed, a treatment solution is dischargedfrom a liquid jet tube toward the inner surface of the cylindricalmember, and part of the treatment solution is made to overflow. Theinner surface treatment apparatus includes a liquid detection sensorthat detects the presence or absence of overflow.

JP-A-11-117092 discloses an anodizing and coating apparatus thatanodizes the cylinder inner surface of a cylinder block.

The Applicant of the present application proposed an anodizing apparatusthat is configured so that a hollow electrode is placed in a hollowsection of a workpiece, and an electrolyte solution jet port is providedthat discharges an electrolyte solution from the hollow section of theelectrode toward the inner surface of the workpiece in a directiondiagonal to the tangential direction of the electrode(JP-A-2005-314751).

However, such a known surface treatment apparatus is designed to beapplied to a workpiece having a circular cross-sectional shape, andcannot uniformly treat the inner surface of a workpiece having a hollowsection, and having a plurality of protrusions and a plurality ofrecesses that are formed on the inner surface thereof.

SUMMARY

An object of the invention is to provide an electrolytic apparatus foruniformly treating the inner surface of a workpiece having a hollowsection, and having a plurality of protrusions and a plurality ofrecesses that are formed on the inner surface thereof, and a surfacetreatment method using the same.

According to one aspect of the invention, there is provided anelectrolytic apparatus that is used for a workpiece having an irregularcross-sectional shape, the workpiece having a hollow section that isformed vertically therethrough, and having a plurality of protrusionsand a plurality of recesses that are formed on an inner surface thereof,the electrolytic apparatus comprising:

a mounting section that closes a lower opening of the workpiece;

a holding section that closes an upper opening of the workpiece; and

an electrode that is placed inside the workpiece,

the electrode having a hollow cross-sectional shape, and having aplurality of jet orifices for discharging an electrolyte solutionrespectively toward the plurality of recesses of the workpiece, and

the mounting section and/or the holding section having a plurality ofdrain outlets that are provided respectively corresponding to theplurality of recesses of the workpiece.

According to another aspect of the invention, there is provided asurface treatment method that utilizes the electrolytic apparatus asdefined in claim 1, the surface treatment method comprising:

closing a lower opening of a workpiece having an irregularcross-sectional shape using the mounting section, the workpiece having ahollow section that is formed vertically therethrough, and having aplurality of protrusions and a plurality of recesses that are formed onan inner surface thereof;

closing an upper opening of the workpiece using the holding section;

connecting the electrode and the workpiece to a power supply forelectrolysis; and

discharging an electrolyte solution from the plurality of jet orificesof the electrode respectively toward the plurality of recesses of theworkpiece to effect electrolysis while discharging the electrolytesolution from the plurality of recesses of the workpiece through theplurality of drain outlets provided to the mounting section and/or theholding section.

The term “electrolytic apparatus” used herein refers to an apparatusthat effects surface treatment using an electrolyte solution throughelectrolysis. The term “electrolytic apparatus” used herein includes anapparatus that effects anodizing using an electrolyte solution ofaluminum, an alloy thereof, magnesium, an alloy thereof, titanium, or analloy thereof, and an apparatus that effects electroplating using aplating solution as an electrolyte solution.

The workpiece to which the invention is applied has a hollow sectionthat is formed therethrough from one end to the other end, and has aplurality of protrusions and a plurality of recesses that are formed onthe inner surface thereof (inside the hollow section) (i.e., the innersurface of the workpiece has an irregular cross-sectional shape).

When a plurality of protrusions and a plurality of recesses are formedon the inner surface of the workpiece (inside the hollow section), theelectrolyte solution does not uniformly flow over the inner surface ofthe workpiece when the electrolyte solution is merely discharged fromthe hollow electrode placed inside the workpiece.

The plurality of protrusions and the plurality of recesses are formed onthe inner surface of the workpiece so that the value “H/D” is within therange of 0.05 to 0.4 (where, H is the height from the bottom of therecess to the top of the protrusion, and D is the diameter of aninscribed circle that is inscribed to the bottom of the recess).

The term “recess” used herein excludes a recess that is formed on eachside or around a protrusion having a value “H/D” of less than 0.05.

According to one aspect of the invention, since the electrolyte solutionis discharged toward the plurality of recesses formed on the innersurface of the workpiece, and a plurality of drain outlets are providedrespectively corresponding to the plurality of recesses, the electrolytesolution flows over the entire inner surface of the workpiece, and localburning due to electrolysis can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of the structure of an electrolyticapparatus (anodizing apparatus) according to one embodiment of theinvention, and FIG. 1B illustrates an example of the shape of a hollowsection of a workpiece, and the arrangement of a jet orifice and a drainoutlet.

FIGS. 2A and 2B illustrate an example of the arrangement of a jetorifice and a drain outlet, wherein FIG. 2A illustrates a case where onedrain outlet is provided, and FIG. 2B illustrates a case where one jetorifice is provided.

FIG. 3 illustrates a thickness measurement target part.

FIG. 4 shows an electrolytic condition and quality evaluation results.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1A and 1B illustrate an example of the structure (configuration)of an electrolytic apparatus according to one embodiment of theinvention.

An electrolytic apparatus 10 includes a mounting section 11 that closesthe lower opening of a workpiece W, and a holding section 12 that closesthe upper opening of the workpiece W, and is configured so that theworkpiece W can be removed by moving one of the holding section 12 andthe mounting section 11 vertically relative to the other.

Although FIG. 1A illustrates an example in which the workpiece W placedon the mounting section 11 is held by the holding section 12 from theupper side, the workpiece W may be placed to have the openings on theright side and the left side, and either side (i.e., the right side orthe left side) of the workpiece W may be held by the mounting section 11and the holding section 12.

A seal member 11 a is provided between the mounting section 11 and theedge of the lower opening of the workpiece W, and a seal member 12 a isprovided between the holding section 12 and the edge of the upperopening of the workpiece W in order to prevent a situation in which anelectrolyte solution leaks through the opening of the workpiece W.

In one embodiment of the invention, a hollow electrode 14 is disposedthrough the holding section 12, and a voltage is applied between theelectrode 14 and the workpiece W from a power supply 16 through wiringmembers 16 a and 16 b.

As illustrated in FIG. 1B, the workpiece W has a cross-sectional shapein which an opening is formed therein in the vertical direction, andfour protrusions 21 to 24 are formed on the inner surface thereof sothat four recesses 31 to 34 are formed.

The number of protrusions is not particularly limited as long as two ormore protrusions are formed. In one embodiment of the invention, theprotrusions are formed in the vertical direction from the upper end tothe lower end of the workpiece W. Note that the protrusions may bepartially formed in the vertical direction.

Four jet orifices 15 a to 15 d are provided so that the electrolytesolution is discharged from the hollow electrode 14 toward the recesses31 to 34 of the workpiece W, and four drain outlets 13 a to 13 d areprovided respectively corresponding to the recesses 31 to 34 so that theelectrolyte solution is discharged from the recesses 31 to 34.

In FIGS. 1A and 1B, the flow of the electrolyte solution isschematically indicated by each arrow.

The electrolyte solution discharged through the drain outlets issupplied to the electrode through a circulating pump and a temperaturecontroller.

The inner surface of the workpiece illustrated in FIG. 3 that was formedof an aluminum alloy was anodized using the electrolytic apparatusillustrated in FIGS. 1A and 1B, and the results were evaluated (seebelow).

The workpiece was anodized using an electrolytic apparatus in which fourjet orifices and four drain outlets were provided (Examples 1 to 4), anelectrolytic apparatus in which four jet orifices and one drain outletwere provided (Comparative Example 1) (see FIG. 2A), or an electrolyticapparatus in which one jet orifice and four drain outlets were provided(Comparative Example 2) (see FIG. 2B).

The diameter D of an inscribed circle inscribed to the bottom of therecess of the workpiece W was about 80 mm, and the height H of theprotrusion of the workpiece W was about 15 mm.

The workpiece W was subjected to a pretreatment (e.g., degreasing)according to a common procedure, and then anodized. A sulfuric acidaqueous solution (concentration: 200 g/L) was used as the electrolytesolution (temperature: 10° C.). The electrolyte solution was dischargedfrom the jet orifice of the electrode, discharged through the drainoutlet, and circulated using a circulating pump.

The anodized workpiece W was washed with hot purified water (70° C.) for3 minutes, and the thickness of the measurement target parts a to d ofthe workpiece W illustrated in FIG. 3, and the hardness of the coatingwere measured.

FIG. 4 (table) shows the electrolytic condition (current density), theflow rate of the electrolyte solution, and the quality evaluationresults.

Note that the thickness of the workpiece W was measured using an eddycurrent thickness gauge, and the hardness of the coating (cross section)was measured using a micro Vickers hardness tester (load: 25 g).

As shown in FIG. 4, the measurement target parts a to d had a uniformthickness, and the coating had a uniform hardness in Example 1 (currentdensity: 1 A/dm² (normal coating-forming condition)) and Examples 2 to 4(current density: 27 or 40 A/dm² (hard coating-forming condition)).

In contrast, the coating was burned (i.e., a normal coating could not beobtained) in Comparative Examples 1 and 2.

Although only some embodiments of the invention have been described indetail above, those skilled in the art will readily appreciate that manymodifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of the invention.Accordingly, all such modifications are intended to be included withinscope of this invention.

What is claimed is:
 1. An electrolytic apparatus that is used for aworkpiece having an irregular cross-sectional shape, the workpiecehaving a hollow section that is formed vertically therethrough, andhaving a plurality of protrusions and a plurality of recesses that areformed on an inner surface thereof, the electrolytic apparatuscomprising: a mounting section that closes a lower opening of theworkpiece; a holding section that closes an upper opening of theworkpiece; and an electrode that is placed inside the workpiece, theelectrode having a hollow cross-sectional shape, and having a pluralityof jet orifices for discharging an electrolyte solution respectivelytoward the plurality of recesses of the workpiece, and the mountingsection and/or the holding section having a plurality of drain outletsthat are provided respectively corresponding to the plurality ofrecesses of the workpiece.
 2. A surface treatment method that utilizesthe electrolytic apparatus as defined in claim 1, the surface treatmentmethod comprising: closing a lower opening of a workpiece having anirregular cross-sectional shape using the mounting section, theworkpiece having a hollow section that is formed verticallytherethrough, and having a plurality of protrusions and a plurality ofrecesses that are formed on an inner surface thereof; closing an upperopening of the workpiece using the holding section; connecting theelectrode and the workpiece to a power supply for electrolysis; anddischarging an electrolyte solution from the plurality of jet orificesof the electrode respectively toward the plurality of recesses of theworkpiece to effect electrolysis while discharging the electrolytesolution from the plurality of recesses of the workpiece through theplurality of drain outlets provided to the mounting section and/or theholding section.